[llvm] ThinLTO: Add flag to print uselistorder in bitcode writer pass (PR #133230)

[Teresa Johnson via llvm-commits]

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@@ -487,9 +488,9 @@ void splitAndWriteThinLTOBitcode(
   // be used in the backends, and use that in the minimized bitcode
   // produced for the full link.
   ModuleHash ModHash = {{0}};
-  W.writeModule(M, /*ShouldPreserveUseListOrder=*/false, &Index,
+  W.writeModule(M, ShouldPreserveUseListOrder, &Index,
                 /*GenerateHash=*/true, &ModHash);
-  W.writeModule(*MergedM, /*ShouldPreserveUseListOrder=*/false, &MergedMIndex);
+  W.writeModule(*MergedM, ShouldPreserveUseListOrder, &MergedMIndex);
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teresajohnson wrote:

This pass is splitting modules into 2 halves, which requires some updates to each part, and is why AARGetter and other things are needed. To test getting a split module, you'll need one with type metadata. For an example, see the `llvm/test/Transforms/ThinLTOBitcodeWriter/split.ll` test. You will know you are successful if you need to use llvm-modextract to get the bitcode out to check it.

> Unfortunately constants also have use lists that need ordering, so the symbols don't matter

So does this mean you need to pass the new parameter through to the WriteBitcodeToFile call on line 287? To test that path see for example `llvm/test/Transforms/ThinLTOBitcodeWriter/unsplittable.ll`.

https://github.com/llvm/llvm-project/pull/133230